Generally, the system in which, for example, an image is captured by an imaging device (image sensor) and is displayed on a display device (which will be referred to as an imaging display system hereinafter) entails the drawback that image quality may vary depending on the light and shade (brightness) of the environment where the image is captured.
However, in the case of a static image to be captured, the image quality can be improved by adjusting the exposure time of the imaging device. In a dark place, for example, the exposure time should be prolonged to secure sufficient quantity of light and thus it is possible to obtain an image with less noise.
On the other hand, in the case of a moving image to be captured, adjustment of exposure time is restricted because of the refresh rate (frame rate). For example, exposure time cannot be made longer than one frame period during which an image of one frame is displayed.
Therefore, in the case of a dark place, it can be considered that exposure time should be prolonged by lowering the refresh rate (prolonging the period of one frame), thereby securing sufficient quantity of light (exposure time).
In this case, however, the time required for the imaging device to scan one frame image (hereafter also referred to as scanning time) for generating image signals for the one frame image must also be changed, which may impose a heavy load on the imaging display system.